Cracks and splits in tree trunks are fairly common and may occur for various reasons, but are usually not a significant threat to the tree.

Usually there’s not much you can do about them once they occur. Tree-trunk cracks and splits, however, occasionally signal a serious problem that may eventually kill the tree.

One of the most common reasons for cracks and splits on tree trunks is frost cracks, which occur during cold winter weather.

When winter temperatures plummet well below normal, especially after a sunny day when the tree trunk has been warmed by the sun’s rays, different expansion rates between the inner and outer wood can cause such a strain in the trunk that a crack develops.

Frost cracks occur suddenly and can be several feet long. Frost cracks appear at a point where the trunk was physically injured.

Maples and sycamores are prone to frost cracks, as are apples, ornamental crabapples, beech, and horse-chestnut.

Isolated trees are more subject to frost cracks than trees in groups or in forest settings. Trees growing on poorly-drained soils are also particularly prone to frost cracks.

Frost cracks often close during summer, only to reopen in succeeding winters. They do not seriously damage trees, although they do provide openings where disease organisms may enter the tree, particularly if the tree is in a weakened condition.

Frost cracks are difficult to prevent. Wrapping the trunks with tree-wrap paper in the fall helps, but is inconvenient to do year after year.

The best way to prevent frost cracks is to prevent any injuries to the trunk throughout the tree’s life. A professional arborist can bolt frost cracks shut with a technique called lip-bolting. Most people simply remove loose bark hanging along the edges of the crack. You should not paint frost cracks or other wounds with tree-wound dressing. These materials can trap moisture, causing decay in the trunk.

Sun scald is another form of winter injury that can cause cracks and splits. Sun scald occurs when cells in the living tissue beneath the bark thaw on sunny days. This occurs mainly on the south or west side of trunks and branches. The cells rupture when they re-freeze at night. The tree is injured when enough cells in a given area rupture. You’ll notice the injury the following spring as a discolored, sunken area. Fungus infections often invade trees via sun-scald injuries.

Young, thin-barked trees are most susceptible to sun-scald injury. These include maple, honey locust, linden, and mountain ash. Heavy pruning on neglected trees exposes sections of bark that have been protected from the sun’s direct rays for years, predisposing them to sun-scald injury.

You can reduce or eliminate sun-scald injury on young trees by wrapping the trunks each fall with tree-wrap paper. Do this every year until the bark begins to roughen. This may take only a few years on some trees, but more years on others. Prune trees that haven’t been pruned for years in stages, not all at once. This will help prevent sun scald.

Other causes of cracks and splits on tree trunks include graft incompatibility and canker infections, two serious problems on certain trees. You’ll need professional help to diagnose these problems. Weak branch angles and physical injury to the trunk from lawn mowers, snowplows, and other equipment may also cause cracks and splits to develop.

“Growing Green” is contributed by Lehigh County Extension Office Staff and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-746-1970.